Stress breaker for dental restorations



y 1957 E. H. ZAHN 2,797,456

STRESS BREAKER FOR DENTAL RESTORATIONS Original Filed Jan. 31, 1955 2 Sheets-Sheet l /A FIG 4 63 FIG 5 53 5/ 684 w 36 49 i w 45 4% ERIC I E VI ENTOR.

July 2, 1957 E, H, ZAHN 2,797,456

STRESS BREAKER FOR DENTAL RESTORATIONS Original Filed Jan. 31, 1955 2 Sheets-Sheet 2 FlG ..8

ERIC H. ZAHN INVENTOR.

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United States Patent 2,797,456 srnnss BREAKER FOR DENTAL RESTORATIONS Eric H. Zahn, Seattle, Wash, assignor to Austenal, Inc Chicago, IlL, a corporation of New York Continuation of application Serial No. 485,138, January 31, 1955. This application August 16, 1956, Serial Nnseassz 9 Claims. (31. 22-160 My invention relates to dental appliances, and, more particularly, to a stress breaker for dental restorations.

The present application is a continuation of my application, Serial No. 485,138, filed January 31, 1955, now abandoned. I

I Briefly, this structure includes a metal pivot member to be cast in the saddle of a restoration section and a wax pivot member to be waxed in a wax clasp pattern and forming a stress breaking connection with the metal pivot member when cast.

Damage is often caused to an abutment tooth when a restoration section for an adjoining ridge of the mouth is rigidly secured thereto by a clasp section. The forming of a stress breaker between the clasp section and saddle can be an exacting, tedious and difiicult operation if the dentist or technician has to form his own hinge or uses a stress breaker that is not well adapted for this use.

The objects of my invention include therefore: to provide an improved stress-breaker to connect the restoration section and the clasp section of a restoration appliance; to provide in such construction nicety of operation, ease and accuracy of installation and economy of manufacture; to provide such a hinged assembly which is particularly adapted to the lost-wax processing of the appliance; and to provide a simple, effective and easily installed abutment limiting movement of the restoration section away from and/ or towards the ridge of the mouth which it covers.

My invention will be best understood, together with additional objectives and advantages thereof, from the following description, read with reference to the drawings, in which:

Figure l is a perspective view of a dental model having mounted thereon a partially constructed rugae bar case and typifying an application of my invention in the production of dental appliances;

Figure 2 is an enlarged fragmentary view in perspective of a stress-breaking construction for distal extensions in dental appliancesaccordingto my invention;

Figure 3 is an enlarged exploded view in perspective of the metallic hinge element and the prepared wax pattern of the mating part;

Figure 4 is a enlarged sectional view of portions of the clasp, stress breaker (in modified form) and saddle in the intermediate step of processing before the appliance is cast in the lost-wax process;

Figure 5 is a view similar to Figure 4 showing the parts after the wax patterns havebeen cast in metalgand Patented July 2, 1957 moved. The location of the restoration could be differcm, i. e., occur only on one side or be secured to a different anterior tooth. The partial denture could be fastened to a rear molar, in which case the denture would extend forward therefrom.

Figure 1 also shows the cast metal denture parts including a rugae bar 22 and tooth clasps 26 and 28. The exemplary showing in Figure 2 of clasp 26 comprises two ring clasp arms 30 and 32 and the occlusal rest 34, all of which are carefully fitted to the abutment tooth 12 so that in the .pati'ents mouth this clasp is stationary. Clasp 28 is similar in construction but not necessarily identical in detail due to variations in tooth form and the exigencies of the undertaking.

Extending between clasp 26 'and clasp 28 is a continuous clasp 24 which is a metallic element of scalloped shape that fits closely to the lingual surfaces of the anteriors and is rigid with the clasp. To impart further rigidity, the rugae bar 22 is shaped to fit the irregular ridges of the hard palate of the lower jaw. Of course the clasp could be formed in different ways, i. e;, a lingual or partial bar shape with integrated saddles, but the stress-breaking mechanism, to be described hereafter, would be the same.

Attached to this framework is the saddle skeleton 36 which comprises the openwork base for a dental restoration such as is shown on the right side of Figure 1 and includes the plastic saddle 38 and restored posterior teeth 40, 42, 44. The saddle skeleton 36 is embedded within the plastic material forming saddle 38.

I prefer to form this framework of a chrome-cobaltmolybdenum alloy, well known commercially, because of its extreme strength even in minute cross-section and its resistance to acids and al'kalies. Gold instead may be used. The metal framework described is formed by the well-known lost-wax process. 1

In Figures 2 and 3 are shown the stress-breaking members employed in Figure 1. A metal pivot member 45 is preformed with a shank 46 and 'a pivot head 50. As shown in Figure 4, a wax saddle pattern 36A is formed around shank 46 and later cast in metal. To insure rigid holding of shank 46 in the metal saddle 36, it is desirable to form some special interengaging means. As shown in Figures 2 to 4, a'pair of opposed lugs 48 is provided for that purpose. In order to insure that shank 46 and lugs 48 are completely enclosed in metalwhen they are cast in saddle 36, a wax box 49 is provided around these parts when delivered to the dentist or technician. When box 49 is waxed in saddle pattern 36A, the shank and lugs will be properly enclosed in wax automatically, without the technician taking notice of this detail.

Pivot head 50 is provided with flat sides, as 52, and has a central lateral through opening 54 in which a journal is to be cast as described hereafter.

In the article of commerce delivered to the dentist or technician, a wax hinge pattern 60A is provided which will later become an integral portion 60 of the metal clasp 2 6. Wax hinge pattern 60A includes an upright abutment plate 62A which later provides a fiat abutment face 63 in the completed metal clasp 26. A pair of cheek plates 64A, 66A extend from abutment plate 62A and cover the flat side surfaces 52 of metal hinge 45. Cheek plates 64A, 66A and abutment plate 62A are strengthened by ribs 67A at their junction. A wax journal 68A extends between the centers of cheek plates 64A, 66A

through journal opening 54 in metal pivot member 45. In the processing to be described hereafter, journal 68A becomes a metal journal 68 and the cheek plates 64A, 66A become metallic cheek plates 64, ,66.

Referring to Figure '4, during the waxing-in process upon a model, and usually after the continuous clasp and rugae bars have been formed in wax, the stressbreaking assembly is waxed in. This is done by means of wax rods and bars that are used to fill and span the space between the wax hinge pattern 60A, the wax clasp pattern 26A and between the wax pattern 36A and the metal shank 46. The underside of shank 46 is spaced slightly from the adjacent under surface of the model so that investment materials may flow thereunder.

Referring to Figure 5, all of the wax parts are then cast in metal including clasp 26, cheek plates 64, 66, journal 68 and saddle 36. This is accomplished with the well-known lost-wax process.

The burning-out operation may be conducted at a temperature of 2000 to 2150 F. (1800 F. for gold) during which operation the wax within the investment is driven 011 and the cavity formed. Plastics of certain types can be substituted for the wax in pattern 60A if they can be evaporated in the lost-wax process without leavingresidual ash, i. e., cellulose triacetate or poly styrene could be used. At this time the exposed portions of the chrome-cobalt-molybdenum hinge member 45 become oxidized on their surfaces to the advantage of the subsequent operation of forming the hinge, e. g., when the metal that becomes cheek plates 64, 66 and journal 68 contacts the metal of pivot head 50 and its journal opening 54, the oxidized surfaces prevent fusion of the pre-formed metal and the cast metal and the parts of the stress breaker are free for pivotal movements.

It will be noted that check plates 64, 66 closely abut the flat side surfaces of pivot head 50 and have a guiding function largely preventing twisting of metal hinge member 45 out of its plane or rotation about journal 68. The abutting guiding surfaces are very broad rela tive to the overall size of the parts. The proportions shown in the specific embodiment are quite satisfactory to provide this guiding function in which the area of the abutting surfaces is approximately three times the area of the cross-section of journal 68.

Another phenomenon of the operation which I have discovered is that the better hinge joints are formed with the male portion cast rather than the female memher. For example, in the casting operation, the male journal 68 contacts upon cooling so as to give small play to the journal 68 in the pre-formed female journal oper1- ing 54. On the other hand, shank 46 being the male member, the fluid metal female counterparts therearound shrink into a tight mechanical joinder as the cast saddle 36 cools.

A further feature is the horn stop 70 on pivot head 50 which abuts the abutment surface 62 cast from the wax abutment plate 62A to prevent movement of the restoration too far away from the ridge of the mouth which it covers. In other words, the under side of saddle 38 should be in contact with the ridge 20 in static conditions with abutment surface 63 pressing against stop 70 limiting movement farther away and the stress breaker permitting some inward movement of the restoration section 38 during mastication as it compresses and displaces the flesh thereunder. It will be observed that this stop is almost automatically located with my stress breaker so that the dentist or technician may readily form and locate the stop.

The construction of Figures 4 and are modified in one respect from the structure shown in Figure 3. The lower corner of pivot head 50 is slightly squared to form an abutment surface at 51. The corresponding lower corner of wax pattern 60A has a removable insert shim 53 (Figure 4) which, when removed, forms a corner space 55. In this way, the stress breaker can be delivered with the horn stop 70 in abutment with the surface of wax pattern 60A which will become abutment face 63 (Figure 5) and with the pivot head lower abutment 51 in contact with shim 53 as shown in Figure 4. Upon removal of the shim, and without other attention of the technician, a proper play, limited by the mucous stop abutment face 63 and the interior of cavity 55, is given to the stress breaker in movement away from the ridge of the mouth in absence of pressure and toward the ridge compressing and displacing the mucosa under saddle 36 under conditions of pressure.

Shim 53 can be varied in thickness to change the amount of play between the abutments. The shim may be formed by a material which will remain in place during the burning out and casting operations in the lost-wax process and then be later removed as by acids or caustic according to the material used for the shim. Good results have been obtained by using a shim formed of refractory material composed of aluminum, silicon and magnesium. This shim may be dissolved out with a strong caustic such as sodium hydroxide after the stress breaker has been cast. However, the preferred construction is to use a shim formed of the same chrome cobalt-molybdenum material as the remainder of the hinge. In this case, the shim will be oxidized during the burning-out of the mold and when the abutting parts are cast they will make only a slight bond with the oxidized shim. The metal shim then can be knocked out at any time, c. g., for convenient processing preferably after the teeth are set in the denture and all other processing is complete. If instead the shim is formed of material to be removed by caustic or acid, the shim should be removed immediately after the stress breaker is cast so that these agencies will not work on other parts of the denture which are not resistant to their action. Instead of a chome-cobalt-molybdenum metal shim, other metals may be substituted, the faces of which will oxidize in the burning-out process and the oxidized faces of which will not fuse with the metal cast to form clasp section 26.

The modified structure of Figures 6 to 8 is generally a reversal of the structure of Figures 4 and 5. For convenience in comparison, the reference numerals used correspond in the two forms, except the Figures 6 to 8 form uses a one hundred series.

As delivered to the dental laboratory, the parts of the stress breaker appear as shown in Figure 6 except that the hinge parts are in engagement. A wax pattern 160A to be waxed in the clasp pattern 126A to form clasp 126 has an upright abutment plate 162A which later forms a flat upper abutment face 163 in the cast assembly to be engaged by abutment means on the other hinge member. A pivot head 164A extends from abutment plate 162A and carries paired central trunnions 168A. A removable shim 153 is embedded in lower face of plate 162A; and when the shim is removed after casting of the appliance, a recess 155 is formed in the plate corner, the inner face of which forming a lower abutment for a lower stop on the other hinge member.

A metal member is engaged with the wax pattern 160A as delivered to the dental laboratory. Metal hinge member 145 has hinge means formed by a pair of cheek plates 150, the inner faces of which abut the sides of pivot head 164 guiding the action of the pivot head. Pivot head 164 is cast from a wax head 164A and tends to shrink in casting thus relieving the guiding surfaces. This forms a looser joint than in the reversed Figures 4 and 5 construction and will be selected by those desiring a more easily moved stress breaker.

Upper and lower horn stops 170, 151 abut the surfaces of plate 162A and shim 153 before casting, as in Figure 7, and later are disposed to act against upper and lower abutment surfaces 163, 155 in the completed article shown in Figure 8. These abutments limit the movement of saddle 36 toward and away from the ridge of the mouth it covers and yet are largely automatically formed in the processing of the stress breaker after the waxing is completed. Cheek plates have paired openings 154 in which the wax pattern and cast trunnions 168A, 168 are positioned. The cast trunnions 168 will shrink slightly on cooling so as to move freely in opening 154.

The axis of the metal shank 146 is preferably above the axis of trunnion opening 154 to position the pont of pivot and the stops properly. Shank 146 bears a pair of lugs 148 which form additional securing means for engagement of the shank in saddle 136 besides the shrinking of the metal of the saddle therearound. Unless the waxing of saddle pattern 136A is done carefully, the wax might be unduly thin about parts of the shank, and this problem is obviated by the formation of a wax box 149 about shank 146 and lugs 148 in manufacture. Wax box 149 will be waxed in place in saddle pattern 136A and no thought need be given to the proper covering of the shank in the saddle. The further processing of the pattern for the stress breaker follows that described with the Figures 4 and 5 construction. As mentioned before, one advantage of this construction is that in each case the male part is cast to the female part in the structure where movement between parts is desired. The reverse is observed in the case of the fixed joinder of saddle to shank.

Having thus described my invention, I do not wish to be limited to the precise details of construction shown but wish instead to cover these modifications thereof within the scope of my invention which will occur to those skilled in the art, as defined in the appended claims.

I claim:

1. Means for forming a stress breaker between a clasp section to be attached to an abutment tooth and the saddle of a restoration section straddling a ridge of the mouth, comprising: a first hinge member having a shank at one end to be anchored in said saddle and a second hinge member having an upright abutment plate, one of said hinge members having a pair of check plates and the other hinge member having a pivot head disposed between said cheek plates, the pivot head and cheek plates having flat abutting side surfaces whereby the cheek plates guide the pivot head in its pivoting and one having central journal means and the other having bearing opening means in which the journal means is positioned forming a pivotal connection between the cheek plates and the pivot head, the first hinge member being formed of metal and the second hinge member being a pattern formed of material normally volatilizable in the lostwax process, said first hinge member having a horn stop positioned to extend outwardly relative said ridge and disposed to pivot into abutting relation to said abutment plate to restrict movement of said saddle away from said ridge.

2. The subject matter of claim 1 in which there is a removable shim embedded in the lower margin of the face of said abutment plate, said first hinge member having a lower mucous stop disposed to abut a wall of the recess forward in said abutment plate upon the removal of said shim to restrict movement of said saddle against the mucosa.

3. The subject matter of claim 2 in which said shim is formed of metal, the faces of which are oxidizable in the volatilization step of the lost-wax process and the oxidized faces of which will not fuse with metal cast to form said second hinge member.

4. The subject matter of claim 2 in which said shim is formed of refractory material which is removable by a strong caustic agent.

5. The subject matter of claim 1 in which said check plates are part of said second hinge member and have a journal extending therebetween forming said journal means and in which said pivot head is a part of said first hinge member and has a central opening in which said journal is disposed forming said bearing opening means.

6. The subject matter of claim 1 in which said check plates are part of said first hinge member and each has a bearing opening forming said bearing opening means and said pivot head is part of said second hinge member and has a pair of central opposed trunnions positioned in said bearing openings forming said journal means, the axis of said shank being disposed above the center of said bearing openings.

7. The subject matter of claim 1 in which there is a box formed around said shank formed of material normally volatilizable in the lost-wax process to insure that the shank is adequately covered when said saddle is waxed 8. Means for forming a stress breaker between a clasp section to be attached to an abutment tooth adjacent a ridge of the mouth and the saddle of a restoration section straddling said ridge, comprising: a first hinge member having a shank at one end to be anchored in said saddle and a second hinge member having an upright abutment plate, one of said hinge members having a journal and the other of said hinge members having a bearing opening in which said journal is positioned thereby forming a pivotal connection therebetween, the first hinge member being formed of metal and the second hinge member being a pattern formed of material normally volatilizable in the lost-wax process, said first hinge member having an outer stop positioned outwardly from said ridge relative the pivotal axis of the stress breaker and having an inner mucous stop positioned inwardly toward said ridge relative the pivotal axis of the stress breaker, said abutment plate having embedded in the lower margin of its face a removable shim and said outer and inner stops being positioned contiguous the upper margin of said abutment plate and said shim respectively, and the lower mucous stop being disposed to pivot into abutment with a wall of the recess formed in said abutment plate upon removal of said shim whereby the permitted pivotal action of the stress breaker is determined principally by the thickness of said shim, said shim being formed of metal the faces of which are oxidizable in the volatilization step of the lost-wax process and the oxidized faces of which will not fuse with metal cast to form said second hinge member whereby said shim may be struck from the cast abutment plate.

9. Means for forming a stress breaker between a clasp section to be attached to an abutment tooth and the saddle of a restoration section straddling a ridge of the mouth, comprising: a .first hinge member having a' shank at one end to be anchored in said saddle, a second hinge member having an upright abutment plate provided with a recess formed therein, one of said hinge members having a pair of side plates and the other hinge member having a pivot head disposed between said side plates, the pivot head and side plates having flat abutting side surfaces whereby the side plates guide the pivot head in its pivoting movement and one having central journal means and the other having bearing opening means in which the journal means is positioned forming a pivotal connection between the side plates and the pivot head, and a stop on said first hinge member and disposed to abut a Wall of the recess in said abutment plate.

No references cited. 

